Gravity-feed watering devices have been used for a number of years in order to provide water for livestock, such as chickens, to drink. In general, the watering device includes a basin having a low wall that defines a drinking trough. A metal or plastic water reservoir is mounted above the basin. Typically, the reservoir has a fluid capacity of one to five gallons.
In use, the reservoir is positioned on the basin such that an open end is downwardly-oriented, akin to a bucket that is turned upside down. In order to fill the watering device, the reservoir is detached from the basin. The reservoir is then inverted so that its open end is exposed. Water may then be filled into the reservoir, which then retains the water. After the reservoir is filled, the basin is reattached to the reservoir, and the device is tipped over, such that the basin is upwardly-oriented and the reservoir is downwardly-oriented. In this orientation, the outer circumferential wall of the basin overhangs the reservoir, as the diameter of the basin exceeds that of the reservoir.
FIG. 1 illustrates a cross-sectional view of a conventional watering device 10. The device 10 includes a basin 12 having base 14 integrally formed with an outer wall 16 defining a water-retaining volume therebetween. The device 10 also includes a reservoir 18 having a base 20 integrally formed with circumferential walls 22. An open end of the reservoir leads to a cavity 24 configured to receive and retain water 26.
As shown in FIG. 1, the device 10 is in an operational configuration such that the reservoir 18 is attached to the basin 12. A drinking trough 28 is defined between the outer wall 16 and the edges of the walls 22.
A channel or notch may be formed proximate the edge of walls 22 of the reservoir 18. The channel allows water to flow by force of gravity from the reservoir 18 into the trough 28. As water flows out of the reservoir 18, it is replaced by air that bubbles past the edge and collects in an air pocket above the water 26 contained within the reservoir 18.
The water 26 inside the reservoir 18 flows into the drinking trough 28 until the water level in the trough 28 rises above the lower edge 30 of the reservoir 18. Accordingly, air is prevented from entering the reservoir 18 to take the place of the water 26. At this point, a vacuum forms above the surface of the water 26 within the reservoir, and ambient air pressure quickly balances the water and air pressure inside the reservoir 18, thereby preventing additional water 26 from flowing into the trough 28.
Watering devices, such as the device 10, are often used outdoors or in unheated buildings, such as chicken coops. In these settings, air temperature may drop below freezing. In order to prevent ice from forming in the watering devices, some individuals opt to employ high wattage light bulbs above the watering devices. Alternatively, or additionally, heated metal bases may be used to heat the water. However, the use of light bulbs may prove very inefficient and ineffective, and heated bases typically cannot be used with plastic watering devices, as such could melt or otherwise damage the plastic.
United States Patent Application Publication No. 2008/0245308, entitled “Heated Poultry Fountain,” filed Apr. 9, 2007 (the “Clark application”), discloses a system that incorporates a heating element into the basin. The heating element covers the underside of the basin and is disposed along an inner wall of the drinking trough. The Clark application recognizes that water in the drinking trough will lose heat much faster than the water within the reservoir due to its smaller volume and direct exposure to ambient air. Accordingly, the Clark application devotes at least 40% of the heating element to heating the trough in order to have a higher wattage per volume of water in that volume. Thus, whenever the heating element is activated, water within the trough is heated to a higher temperature.
In a system such as disclosed in the Clark application, however, the thermostat that controls the power supplied to the heating element is positioned to monitor the temperature of the reservoir. Because the mass of water in the reservoir may be 30-50 times greater than the mass of water in the drinking trough, and the water in the reservoir is insulated to a certain degree, while the water in the trough is not, the rate of heat loss for water in the trough may be several orders of magnitude greater than for that in the reservoir. Hence, water in the trough cools much quicker than water within the reservoir.
For example, suppose the thermostat is set to activate when the water temperature reaches 4° C. Typical thermostats exhibit a hysteresis of around 10° C., so it is safe to assume that the water in the reservoir may have been initially 14° C. or higher. Assuming that the water in the drinking trough is heated to a much higher temperature because of the higher wattage per unit water volume around the trough, the water temperature in the trough may be as high as 40° C.
The rate of heat loss is given be the following equation:Q=mcΔ/Δt 
where Q is the rate of heat loss, m is the mass of the water, c is the specific heat of water, ΔT is the change in temperature, and Δt is the length of time.
Assuming a best-case condition in which the rate of heat loss for water within the reservoir and the trough is the same, the equations for the reservoir and the trough may be set to equal one another:Q1=Q2 m1cΔT1/Δt=m2cΔT2/Δt 
Using a one gallon reservoir as an example, the mass of the water in the reservoir may typically be around 10 times the mass of the water in the drinking trough. That is, m1=10m2. Thus,10m2cΔT1/Δt=m2cΔT2/Δt ΔT2/Δt=10ΔT1/Δt 
Therefore, in best-case conditions, when the rate of heat loss is the same for both the reservoir and the drinking trough, the rate of temperature change for the water in the drinking trough will be 10 times faster than for the water in the reservoir. Accordingly, the water in the reservoir may cool to 10° C., while the water in the trough is already freezing.
In actual conditions, however, the rate of heat loss for water in the drinking trough is typically much higher than that within the reservoir, so the discrepancy noted above is exacerbated. To compensate, the set point of the thermostat is typically much higher (for example, 16° C.). Then, while the water in the reservoir varies from 16° C. to 26° C., the water in the drinking trough varies from 0° C. to 40° C. Maintenance of water temperature at such an artificially high temperature is inefficient and costly.
Additionally, the higher temperature to which the water is heated increases the rate of evaporation. Therefore, the reservoir typically needs to be refilled frequently. Moreover, hotter water is less desirable for drinking, even by livestock.
If the thermostat is moved from the reservoir to the trough, the heating element may shut off too soon before enough heat is delivered to the reservoir. As a result, water within the reservoir may freeze and possibly cracker the reservoir.